Abstract

A large proportion of pharmaceutical compounds exhibit poor water solubility, impacting their delivery. These compounds can be passively encapsulated in the lipid bilayer of liposomes to improve their water solubility, but the loading capacity and stability are poor, leading to burst drug leakage. The solvent-assisted active loading technology (SALT) was developed to promote active loading of poorly soluble drugs in the liposomal core to improve the encapsulation efficiency and formulation stability. By adding a small volume (~5 vol%) of a water miscible solvent to the liposomal loading mixture, we achieved complete, rapid loading of a range of poorly soluble compounds and attained a high drug-to-lipid ratio with stable drug retention. This led to improvements in the circulation half-life, tolerability, and efficacy profiles. In this mini-review, we summarize our results from three studies demonstrating that SALT is a robust and versatile platform to improve active loading of poorly water-soluble compounds. We have validated SALT as a tool for improving drug solubility, liposomal loading efficiency and retention, stability, palatability, and pharmacokinetics (PK), while retaining the ability of the compounds to exert pharmacological effects.

Abstract

The solvent-assisted active loading technology (SALT) was developed for encapsulating a water insoluble weak base into the liposomal core in the presence of 5% DMSO. In this study, we further examined the effect of various water miscible solvents in promoting active loading of other types of drugs into liposomes. To achieve complete drug loading, the amount of solvent required must result in complete drug solubilization and membrane permeability enhancement, but must be below the threshold that induces liposomal aggregation or causes bilayer disruption. We then used the SALT to load gambogic acid (GA, an insoluble model drug that shows promising anticancer effect) into liposomes, and optimized the loading gradient and lipid composition to prepare a stable formulation (Lipo-GA) that displayed >95% drug retention after incubation with serum for 3 days. Lipo-GA contained a high drug-to-lipid ratio of 1/5 (w/w) with a mean particle size of ?75?nm. It also displayed a prolonged circulation half-life (1.5?h vs. 18.6?h) and enhanced antitumor activity in two syngeneic mice models compared to free GA. Particularly, complete tumor regression was observed in the EMT6 tumor model for 14?d with significant inhibition of multiple oncogenes including HIF-1?, VEGF-A, STAT3, BCL-2, and NF-?B.

Abstract

A variety of nanoplatforms have been developed and applied for cancer therapy, imaging, or the combination thereof. These nanoplatforms, combined with therapeutic and imaging functionalities, display great potential to enhance medical care. In particular, lipid-based nanoparticles (LNPs) are among the most-studied platforms that have resulted in many encouraging advances in theranostics. LNPs are biodegradable and biocompatible, and their formulation can be tailored for various applications. Here, we provide an overview of recent developments of four representative LNP platforms for theranostics: stealth liposomes, triggered-release liposomes, porphysomes, and lipid-coated calcium phosphate NPs (LCPs). We discuss their potential, limitations, and potential applications for cancer care and highlight perspectives and future directions for the nanotheranostics field.

Abstract

Mefloquine (Mef), a poorly soluble and highly bitter drug, has been used for malaria prophylaxis and treatment. The dosage form for Mef is mostly available as adult tablets, and thus children under the age of 5 suffer from poor medication adherence. We have developed a stable, rapidly dissolvable, and palatable pediatric formulation for Mef using liposomes composed of 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) and cholesterol with a mean diameter of ?110 nm. Mef was actively loaded into the liposomes via an ammonium sulfate gradient using the solvent-assisted loading technology (SALT) developed in our lab. Complete loading of Mef inside the liposomal core was achieved at a high drug-to-lipid ratio (D/L) of 0.1-0.2 (w/w), and the final drug content in the formulation was ?8 mg/mL, well above the solubility of Mef (<0.6 mg/mL in simulated fluids). The strong bitterness of Mef was masked by the liposomal encapsulation as measured by an electronic tongue. Incubating the Mef-liposomes (Mef-Lipo) in the simulated gastric fluid (pH 1.2) and the simulated intestinal fluid containing 3 mM sodium taurocholate (pH 6.8) induced changes in liposome size and the polydispersity, resulting in drug release (?40% in 2 h). However, no drug release from the Mef-Lipo was measured in the bile salt-free intestinal fluid or simulated saliva (0% in 3 h). These data suggest that drug release from the Mef-Lipo was mediated by a low pH and the presence of a surfactant. Pancreatic lipase did not degrade DSPC in the Mef-Lipo after 8 h of incubation nor induce Mef release from the liposomes, indicating that lipid digestion played a minor role for drug release from the Mef-Lipo. In order to improve long-term room temperature storage, the Mef-Lipo was lyophilized to obtain a solid formulation, which was completely dissolvable in water in 10 s and displayed similar in vitro profiles of release as the liquid form. The lyophilized Mef-Lipo was stable at room temperature for >3 months. In mice, orally delivered liquid and lyophilized Mef-Lipo displayed comparable absorption with bioavailability (BA) of 81-86%, while the absorption of the standard Mef suspension was significantly lower with BA of 70% and 20% decreased maximal plasma concentration and area under the curve. Our data suggest that the Mef-Lipo was a stable, palatable, and bioavailable formulation that might be suitable for pediatric use.

Abstract

This study was aimed at developing a new active loading method to stably encapsulate staurosporine (STS), a water insoluble drug, into lipid-based nanoparticles (LNPs) for drug targeting to tumors.A limited amount of DMSO was included during the active loading process to prevent precipitation and facilitate the loading of insoluble STS into the aqueous core of a LNP. The drug loading kinetics under various conditions was studied and the STS-LNPs were characterized by size, drug-to-lipid ratio, drug release kinetics and in vitro potency. The antitumor efficacy of the STS-LNPs was compared with free STS in a mouse model.The drug loading efficiency reached 100% within 15 min of incubation at a drug-to-lipid ratio of 0.31 (mol) via an ammonium gradient. STS formed nano-aggregates inside the aqueous core of the LNPs and was stably retained upon storage and in the presence of serum. A 3-fold higher dose of the STS-LNPs could be tolerated by BALB/c mice compared with free STS, leading to nearly complete growth inhibition of a multidrug resistant breast tumor, while free STS only exhibited moderate activity.This simple and efficient drug loading method produced a stable LNP formulation for STS that was effective for cancer treatment.

Abstract

We have developed a polymer conjugate (Cellax) composed of acetylated carboxymethylcellulose (CMC), docetaxel (DTX), and PEG, designed to enhance the pharmacokinetics (PK) and antitumor efficacy of DTX. Our design placed an emphasis on nanoparticle self-assembly to protect DTX during blood transport, stability of the nanoparticle, and PEGylation to enhance PK. Compared to Taxotere, Cellax exhibited a 38.6 times greater area under the curve (AUC), and significantly lower clearance (2.5%) in PK. Less than 10% of DTX was released from Cellax in the blood circulation, indicating that Cellax were stable during blood transport. Cellax reduced non-specific distribution of DTX to the heart, lung and kidney by 48, 90, and 90%, respectively, at 3 h, compared to Taxotere. The uptake of Cellax at 3 h in the liver and spleen was high (15-45 ?g DTX/g) but declined rapidly to <10 ?g DTX/g in 24 h, and induced no measurable toxicity at 170 mg DTX/kg. Taxotere, on the other hand, displayed non-specific uptake in all the examined normal tissues and induced significant apoptosis in the lung and kidney at 40 mg DTX/kg. The tumor uptake of Cellax was 5.5-fold more than that by Taxotere and the uptake occurred within 3 h after injection and persisted for 10 days. The conjugate exhibited enhanced efficacy in a panel of primary and metastatic mouse tumor models. These results clearly demonstrated that Cellax improved the pharmacokinetics, biodistribution and efficacy of DTX compared to Taxotere with reduced toxicity.

Abstract

A nanoparticle formulation of docetaxel (DTX) was designed to address the strengths and limitations of current taxane delivery systems: PEGylation, high drug conjugation efficiency (>30 wt %), a slow-release mechanism, and a well-defined and stable nanoparticle identity were identified as critical design parameters. The polymer conjugate was synthesized with carboxymethylcellulose (CMC), an established pharmaceutical excipient characterized by a high density of carboxylate groups permitting increased conjugation of a drug. CMC was chemically modified through acetylation to eliminate its gelling properties and to improve solvent solubility, enabling high yield and reproducible conjugation of DTX and poly(ethylene glycol) (PEG). The optimal conjugate formulation (Cellax) contained 37.1 ± 1.5 wt % DTX and 4.7 ± 0.8 wt % PEG, exhibited a low critical aggregation concentration of 0.6 ?g/mL, and formed 118-134 nm spherical nanoparticles stable against dilution. Conjugate compositions with a DTX degree of substitution (DS) outside the 12.3-20.8 mol % range failed to form discrete nanoparticles, emphasizing the importance of hydrophobic and hydrophilic balance in molecular design. Cellax nanoparticles released DTX in serum with near zero order kinetics (100% in 3 weeks), was internalized in murine and human cancer cells, and induced significantly higher toxic effects against a panel of tumor cell lines (2- to 40-fold lower IC50 values) compared to free DTX.